[FIX] web_editor: insert br within a p
[FIX] web_editor: insert br within a p

Have a fieldHTML as:
```
<p>
Some text
<br>
<br>
More text
</p>
```

In the Html field widget, place your cursor before the "M"
press Enter to insert a newline

Before this commit "Some text" and the subsequent `<br>` were deleted
This was because the code:
- split the original `<p>` into two
( i.e. it became
```
<p>
Some text
<br>
<br>
</p>
<p>
More text
</p>
```
)
- took the last child of the first p, which is a text then fell back to the first p
- replaced the whole p with <br>

After this commit, the original p is still split, but we append the br to it instead of replacing it

closes odoo/odoo#32777

Signed-off-by: Lucas Perais (lpe) <42d29efea96f3992aa24782120ec2948e42548fa@odoo.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo